The invention relates to vacuum cleaners, particularly hand-held vacuum cleaners.
More particularly, the invention relates to vacuum cleaners of the type in which the space accommodating the drive motor is separate from the interior of the blower unit, so that the dust-laden air passing through the blower unit will not contact the drive motor.
Vacuum cleaners of this general type are known. It is known to take the housing frame of such a vacuum cleaner and spray it around with hard foam material, the outer skin being made of a flexible material. At the same time, the motor and the blower unit are secured onto the housing frame and encased in hard foam material. The foam material in the vicinity of the air discharge outlet should be of larger pore size than elsewhere, in order to permit the sound-muffled and filtered air to leave the housing at this location.
This known expedient is disadvantageous. Despite the purification of the air by means of a filter bag, fine dust particles are carried along and pass, together with the motor cooling air, over the drive motor. Because the large-pore-sized foam of the discharge outlet region of the housing acts as a supplemental after-connected filter, these fine particles become deposited in the interstices between the foam pores and gradually damp the through-flow of air. This action adds to the already present disadvantage that the expedient of direct encasing in foam material impedes the flow of air, to begin with. After a long period of use, the requisite cooling action for the motor no longer occurs.
It is also known to separate the part of the interior space of the housing containing the motor unit from the part containing the blower unit. This is done to separate the dust-laden air flow of the blower unit from the cooling air flow for the motor unit. The motor is provided with a separate impeller for sucking in ambient air, and such air is passed over the motor to cool it and then discharged back into the atmosphere. The air passing through the blower unit, on the other hand, is sucked into the vacuum cleaner housing through an altogether different and independent opening and then discharged therefrom through another opening likewise independent from the discharge opening for the motor cooling air.
A disadvantage of this known expedient is that cool ambient air must be continually sucked into contact with the motor and then, after it becomes heated as a result of such contact and laden with carbon dust discharged from the motor, returned to the outside. Additionally, this system can be used in vacuum cleaners only when inlet filters are employed.